1. Field of the Invention
The present invention relates to a wavelength division multiplexing (WDM) system, and more particularly to a WDM switch which includes an optical add/drop multiplexer (OADM) and control method thereof.
2. Background of the Related Art
In an optical communication network, a wavelength division multiplexing (WDM) system transmits a plurality of optical signals simultaneously using various wavelengths. This enables the communication network to operate efficiently and at very high speed. Thus networks of this type are suitable for many broadband applications.
When an optical path having a specific wavelength is terminated at a specific node of an optical communication network employing a WDM system, the node should drop the wavelength. Moreover, if it is necessary to setup an optical path at the specific node using a new wavelength, the node uses a wavelength which will not bring about wave collision with signals transmitted on an optical path to another node. This is usually accomplished by having the node add the wavelength to other wavelengths which are passing by the specific node.
There are two kinds of mechanisms for adding/dropping a specific wavelength in a WDM system. The first mechanism operates based on the diffraction grating principle that diffraction/reflection varies in accordance with wavelength. The second mechanism operates by filtering a wavelength using a dichroic filter. At least one embodiment of the present invention includes an optical add/drop multiplexer (OADM) which operates in accordance with the first mechanism, for instance, an coupler-type OADM.
FIG. 1 is a diagram which illustrates a grating used in a coupler-type OADM according to a related art. In this circuit, when an UV (ultraviolet) beam is irradiated on a fusion-type coupler 10 including a photosensitive material through a phase mask, interference patterns are generated so that gratings 30 are formed in the coupler 10 by a photosensitive effect. Such a method of forming gratings in a coupler-type OADM can be applied to an optical waveguide-type coupler as well. As an alternative to the aforementioned technique, etching can be used to form the gratings in an optical waveguide-type coupler.
FIG. 2 is a diagram of a coupler-type OADM according to a related art. In this circuit, when optical signals are input into an input port 50 of an optical waveguide-type coupler 10, an optical signal having a specific wavelength is dropped from the input optical signals by a grating 45 formed at the optical waveguide type coupler 10 with a predetermined period so as to be outputted through a drop port 55. Moreover, when an optical signal having a specific wavelength is inputted to an add port 65 of the optical waveguide type coupler 40, the coupler type OADM according to the related art adds the optical signal having the specific wavelength to an optical signal passing the optical waveguide type coupler 40 by the grating 45, so as to output the added optical signals through an output port 60.
An output wavelength (drop wavelength) of the drop port 55 and an input wavelength (add wavelength) of the add port 65 in the coupler-type OADM are determined by the following Formula 1:
xcex1=2neffxcex91xe2x80x83xe2x80x83[1]
where xcex1, neff, and xcex91 indicate an input/output wavelength (drop/add wavelength), an effective refractive index, and a grating period respectively.
FIGS. 3(a)-(e) are graphs of optical signals having wavelengths dropped/added in a coupler-type OADM according to a related art. In these figures, an optical signal xcex1 (FIG. 3(b)), suitable for satisfying the condition of Formula 1 among optical signals xcex1, xcex2xcex3, . . . , xcexn (FIG. 3(a)) input into an input port 50, is dropped so as to be output to a drop port 55. The rest of the optical signals (FIG. 3(c)) except optical signal xcex1 pass through an optical waveguide-type coupler 40. Once the optical signal xcex1 (FIG. 3(d)) having a wavelength suitable for satisfying the condition of Formula 1 is input into an add port 65, the input optical signal xcex1 (FIG. 3(d)) is added to an optical signal passing through the optical waveguide-type coupler so as to be output to an output port 60 (FIG. 3(e)).
One drawback of the related art is that the grating of the coupler-type OADM cannot be eliminated and still function as intended. Thus, if a function of dropping/adding an optical signal of a specific wavelength is unnecessary, additional manual work is required to remove the coupler-type OADM or the output of the drop port must be returned back to the input of the add port. Because manual work is required to modify or eliminate the coupler-type OADM, it is very difficult to operate this device by remote control. In addition, the coupler-type OADM fails to be flexible to network variation, and thus has poor adaptability when the structure of WDM network frequently varies due to rapid increases in the amount of data.
An object of the invention is provide a wavelength division multiplexing (WDM) system that substantially obviates one or more problems and/or disadvantages of the related art.
Another object of the present invention is to provide an OADM in a WDM system which freely forms/eliminates a grating of an optical waveguide-type coupler constituting the OADM.
Another object of the present invention is to provide an OADM in a WDM system which is suitable for being remotely controlled.
A further object of the present invention is to provide an OADM in a WDM system which drops/adds a plurality of channels simultaneously, by connecting a plurality of remotely controllable 1-channel OADMs in series.
Another object of the present invention is to provide a WDM switching system and method which connects different WDM networks by controlling a WDM switch which includes a multi-channel OADM.
These and other objects and advantages of the present invention are achieved by providing a WDM switching system which includes: a plurality of multi-channel OADMs connected in parallel and having drop and add ports which can be connected to cross with each other, and switching unit for switching a corresponding channel in accordance with an operation control signal for each channel, wherein each of the multi-channel OADMs has drop and add ports.
In another aspect of the present invention, a multi-channel OADM in a WDM system includes a plurality of 1-channel OADMs connected in series, each of the 1-channel OADMs dropping or adding different channels from an input WDM optical signal in accordance with operation control signals for the channels, respectively.
In a further aspect of the present invention, a 1-channel OADM in a WDM system includes first and second conductors arranged periodically so as to have a pair of different polarities, an optical waveguide-type coupler dropping or adding an optical signal of a specific channel by an electric field generated from the first and second conductors, a power supply unit supplying the second conductor with a power, and a switch placed between the second conductor and power supply unit to control a power supply of the second conductor, so as to control generation and termination of the electric field in accordance with an operation control signal.
In a further aspect of the present invention, a method of controlling a 1-channel OADM in a WDM system includes checking whether a drop/add operation is demanded or not, forming an electric field at an optical waveguide-type coupler if the drop/add operation is demanded, and carrying out the drop/add operation of a channel by the formed electric field.
In another aspect of the present invention, a method of controlling a multi-channel OADM in a WDM system includes checking channels to be dropped/added, outputting operation control signals for activating OADMs of channels to be dropped/added, activating the OADMs which receive the operation control signals for activation, and dropping or adding the corresponding channels by the activated OADMs.
In another aspect of the present invention, a method of controlling a WDM switch includes checking channels to be switched to a different WDM network, activating a first OADM dropping the channel to be switched and a second OADM adding the dropped channel, and adding the channel dropped from the second OADM if the corresponding channel is dropped from the first OADM so as to switch the corresponding channel to the different WDM network.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.